1. Field Of The Invention:
This invention generally concerns valves of the type with means to increase head and seat contact pressure and more specifically the type having a piston with expansible packing.
2. Description Of The Prior Art:
Generally, waste accumulated during aircraft passenger flights is held in a collecting tank until, after landing, airport facilities are used to drain the waste from the tanks. To drain the waste, a port is provided in a convenient location in the aircraft fuselage. A removable plug is inserted into the drain port for maintaining the waste in the tank. Prior to draining the tank, the plug obviously must be removed.
In order to achieve plug removal, a bi-conduit valve and plug assembly was devised. In this prior art arrangement the valve was fitted to the port and a key was used to remove and retract the plug into one of the valve conduits while the waste was drained through the other conduit of the valve. While this arrangement is generally satisfactory the plug has presented some problems.
The plug of the prior art valve is generally annular including a radially expandable resilient sealing member sandwiched between opposed rigid plates. The plates are axially movable relative to each other so that when the plates are drawn toward each other, the resilient member is axially compressed between the plates which results in its radial expansion. With little tolerance between the annular inner periphery of the port prior to expansion, only slight radial expansion of the resilient member is required to urge the outer annular periphery of the resilient member into sealing engagement within the port.
One problem associated with such plugs has involved certain difficulty experienced by ground crew personnel in reinserting the plug into the port after the tank is drained. The opposed plate which is first inserted into the port will sometimes "hand-up" on the port sidewall so as to make plug reentry into the port difficult. Also, should the plug be misaligned in the port, it is still possible to actuate the plug locking mechanism so that in effect the ground crewman thinks the plug is properly seated and licked in the port when, in fact, the plug is misaligned in the port and the locking mechanism may become jammed.
Another disadvantage of the known plug is its prohibitive cost due to its rather complex cam operated mechanism used to axially move the opposed plates toward and away from each other.
It would be advantageous to have a novel plug which is capable of providing a proper seal in the port without the common problems associated with the prior art plug.